Tin plating bath having organic compound

ABSTRACT

A BATH FOR TIN PLATING HAVING AN AQUEOUS ACIDIC SOLUTION OF STANNOUS SULFATE AND MINOR PROPORTION OF AN ORGANIC DYE WHICH PROVIDES IMPROVED SOLDERABILITY OF A PART PLATED IN SAID BATH. THE ORGANIC DYE COLORS THE TIN PLATING BATH TO PERMIT COLOR ANALYSIS FOR REPLENISHING THE DYE DURING USE OF THE PLATING BATH. TYPICAL OF SUCH DYES ARE SAFRANINE O, SAFRANINE T, JANUS GREEN B, JANUS BLACK, JANUS GRAY, JANUS BLUE G, JANUS RED AND JANUS YELLOW.

United States Patent 3,585,114 TIN PLATIN G BATH HAVING ORGANIC COMPOUND Henry K. Wren and William T. Hobson, Indianapolis, Ind., assignors to the United States of America as represented by the Secretary of the Navy No Drawing. Filed May 14, 1969, Ser. No. 824,669 Int. Cl. C23b 5/14, 5/46 US. Cl. 204-54 5 Claims ABSTRACT OF THE DISCLOSURE A bath for tin plating having an aqueous acidic solution of stannous sulfate and minor proportion of an organic dye which provides improved solderability of a part plated in said bath. The organic dye colors the tin plating bath to permit color analysis for replenishing the dye during use of the plating bath. Typical of such dyes are safranine O, safranine T, Janus Green B, Janus Black, Janus Gray, Janus Blue G, Janus Red and Janus Yellow.

STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The present invention relates to tin plating baths and more particularly to a bath for tin plating an object which is to be soldered.

Generally, acid tin baths are preferred over alkaline baths for plating as these acid baths can be operated at room temperature and at much higher current densities than can alkaline baths. Without the addition of some organic agent to an acid bath, however, the tin deposits consist of loose crystals or needle-like trees and the base metal is incompletely covered. The presence of these organic additives present a problem during soldering an outgases and released during the heating and melting of the tin plate. These outgases cause bubbles and also the soldered joints are not structurally sound.

SUMMARY OF THE INVENTION The present invention relates to a tin plating bath which will improve solderability of a plated product by the addition of an organic additive which can be continually monitored by colorimetric analysis.

The bath of the present invention is an aq eous acidic solution of stannous sulfate to which between 0.05 and g./liter of an organic additive is added such as safranine O, safranine T, Janus Green B, Janus Black, Janus Gray, Janus Blue G, Janus Red and Janus Yellow. Small amounts of stabilizer, such as hydroquinone, and of a wetting agent can be added to improve the plating bath.

It is therefore a general object of the present invention to provide a tin plating bath which will produce a plated surface which is highly ductile and which has improved solderability.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the present invention, it has been found that certain specific organic agents can be added to an aqueous acidic solution of stannous sulfate which will not cause gaseous bubbles or voids in a plated surface during a soldering operation on the plated surface. Plating solutions have been formulated using, as the organic additive, safranine O, safranine T, and the phenyl azine dyes such as Janus Green B, Janus Black, Janus Gray, Janus Blue G, Janus Red and Janus Yellow.

Various surface active agents can be added to the bath in order to provide better dispersion of tin and other additives in the plating solution. Among those that have been used successfully are the nonyl phenol ethylene oxide condensates, such as Igepal CO-630, which is produced by General Aniline and Film Corp, New York, N.Y., polyalkylene glycol ether, sodium sulfate derivative 2-ethyl l-hexanol, organic phonphate, and aliphatic polyester.

A most significant discovery was made in the formulation of aqueous acidic solutions of stannous sulfate baths, in that highly successful tin plates were deposited from baths containing as little as 2 g./liter of stannous sulfate when one or more of the above-listed organic additives were present. For the upper range, successful plating was accomplished in baths containing 30 g./liter of stannous sulfate. Additionally, these stannous sulfate baths had excellent throwing power as demonstrated by plating in a 1000 ml. Hull Cell bath.

The following plating baths are given by way of example to illustrate the invention in greater detail.

EXAMPLE I G./l. H 153 SnSO 15 Janus Green B 0.5

Surface active agent, 1 mL/l.

A 1000 ml. Hull Cell bath was prepared, and a steel test panel approximately 3% inches by 5 inches and .010 inch thick was plated in the Hull Cell bath at 3 amperes of current for a period of five minutes. The starting temperature of the bath was 109 degrees F. and the temperature of the bath after five minutes was 115 degrees F. The surface active agent used was Antarox BL-225, a product of General Aniline and Film Corp, New York, N.Y. The plated panel had a matte white appearance over the full current density range and there was good coverage on the back of the panel.

EXAMPLE II G./l. H 80 155 SnSO l5 Janus Yellow 1 Hydroquinone 0.5

Surface active agen, l mL/l.

A 1000 ml. Hull Cell bath was prepared and a test panel was plated as in Example I, at 3 amps. The starting temperature was 114 degrees F. and the final temperature was 112 degrees F. The surface active agent was Igepal 00-630, a product of General Aniline and Film Corp. The plate panel was of matte white appearance and acceptable over the entire current density range. Also, there was complete coverage on the back of the test panel.

EXAMPLE III G./l. H 80 155 SnSO 15 Janus Red 0.5 Hydroquinone 0.75

Igepal CO-630, l ml./l.

A test panel was plated as in Example II, with starting temperature being degrees F. and the final temperature being degrees F. The plated panel was matte white in appearance over the entire current density range and on both sides of the panel.

EXAMPLE IV H 50 155 SnSO, 7.5 Janus Blue G 0.5

Hydroquinone 0.5

Igepal CO-630, 1 ml./l.

A 1000 ml. Hull Cell bath was prepared and a test panel was plated at 3 amperes for minutes. The starting temperature was 108 degrees F. and the final temperature was 109 degrees F. The plated panel was matte white and acceptable for the entire current density range on both sides.

EXAMPLE V H 80 166 $11504 2 Janus Green B 0.5 Hydroquinone 0.5

Igepal CO630, 1.0 ml./l.

A 1000 ml. Hull Cell bath was prepared and a test panel was plated at 3 amperes for 5 minutes. The plated panel had a pleasing matte white appearance over the entire density range on both sides of the panel.

EXAMPLE VI A test panel was plated in the bath of Example V for 30 minutes at 5 amperes. The thickness of the plated material averaged about .0011 inch and was uniformly deposited onto the test panel. The plated panel was of a frosty white appearance over the entire current density range on both sides of the test panel.

It is significant to note that the plating bath of Example V contained only 2 g./l. of SnSO yet, highly satisfactory plating was accomplished in a Hull Cell over the entire current density range. The plated tin was heated to reflow temperature, as in a soldering operation, and no undesirable outgassing resulted. Furthermore, the

tin coatings were highly ductile thus lessening the changes of rupture during forming or other manufacturing processes.

The tin plating baths of the present invention have another advantage as the quantity of organic additive present in a particular bath can be measured by a colorimetric procedure. For example, a 10 ml. sample of a bath containing Janus Green B can be measured for transmittancy at 650 nanometers and compared with a standard curve prepared by using a stock plating solution with known amounts of Janus Green B for which transmittancy was plotted versus concentration.

We claim:

1. In an aqueous acidic tin electroplating bath, the improvement wherein there is present an organic additive selected from the group consisting of safranine O, safranine T, Janus Green B, Janus Black, Janus Gray, Janus Blue G, Janus Red and Janus Yellow in an amount sufficient to provide a tin electrodeposit having improved solderability.

2. In an acidic tin plating bath as set forth in claim 1 wherein said organic additive is present in the amount of between 0.05 and 10 g. per liter of tin plating bath.

3. In an acidic tin plating bath as set forth in claim 1, further including a surface active agent.

4. In an acidic tin plating as set forth in claim 1, further including hydroquinone as a stabilizer.

5. In an acidic tin plating bath as set forth in claim 1 wherein said organic additive is Janus Green B and is between 0.05 and 10 g. per liter of tin plating bath.

References Cited UNITED STATES PATENTS 2,460,252 1/1949 DuRose et al 20443 2,846,381 8/1958 Frick et al. 20454 3,141,836 7/1964 Seyb et al. 204-43 GERALD L. KAPLAN, Primary Examiner US. Cl. X.R. 204DIG 2 

